[PATCH 78/85] arm64: KVM: Allow mapping of vectors outside of the RAM region
Marc Zyngier
marc.zyngier at arm.com
Wed Mar 28 05:52:47 PDT 2018
We're now ready to map our vectors in weird and wonderful locations.
On enabling ARM64_HARDEN_EL2_VECTORS, a vector slot gets allocated
if this hasn't been already done via ARM64_HARDEN_BRANCH_PREDICTOR
and gets mapped outside of the normal RAM region, next to the
idmap.
That way, being able to obtain VBAR_EL2 doesn't reveal the mapping
of the rest of the hypervisor code.
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
Documentation/arm64/memory.txt | 3 +-
arch/arm64/Kconfig | 16 +++++++++
arch/arm64/include/asm/kvm_mmu.h | 78 +++++++++++++++++++++++++++++++++++-----
arch/arm64/include/asm/mmu.h | 5 ++-
arch/arm64/kvm/Kconfig | 2 +-
arch/arm64/kvm/va_layout.c | 3 ++
6 files changed, 95 insertions(+), 12 deletions(-)
diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt
index c58cc5dbe667..c5dab30d3389 100644
--- a/Documentation/arm64/memory.txt
+++ b/Documentation/arm64/memory.txt
@@ -90,7 +90,8 @@ When using KVM without the Virtualization Host Extensions, the
hypervisor maps kernel pages in EL2 at a fixed (and potentially
random) offset from the linear mapping. See the kern_hyp_va macro and
kvm_update_va_mask function for more details. MMIO devices such as
-GICv2 gets mapped next to the HYP idmap page.
+GICv2 gets mapped next to the HYP idmap page, as do vectors when
+ARM64_HARDEN_EL2_VECTORS is selected for particular CPUs.
When using KVM with the Virtualization Host Extensions, no additional
mappings are created, since the host kernel runs directly in EL2.
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7381eeb7ef8e..48ad7ca23f39 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -904,6 +904,22 @@ config HARDEN_BRANCH_PREDICTOR
If unsure, say Y.
+config HARDEN_EL2_VECTORS
+ bool "Harden EL2 vector mapping against system register leak" if EXPERT
+ default y
+ help
+ Speculation attacks against some high-performance processors can
+ be used to leak privileged information such as the vector base
+ register, resulting in a potential defeat of the EL2 layout
+ randomization.
+
+ This config option will map the vectors to a fixed location,
+ independent of the EL2 code mapping, so that revealing VBAR_EL2
+ to an attacker does not give away any extra information. This
+ only gets enabled on affected CPUs.
+
+ If unsure, say Y.
+
menuconfig ARMV8_DEPRECATED
bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on COMPAT
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index eb04437d50fa..082110993647 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -360,31 +360,91 @@ static inline unsigned int kvm_get_vmid_bits(void)
return (cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR1_VMIDBITS_SHIFT) == 2) ? 16 : 8;
}
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+#ifdef CONFIG_KVM_INDIRECT_VECTORS
+/*
+ * EL2 vectors can be mapped and rerouted in a number of ways,
+ * depending on the kernel configuration and CPU present:
+ *
+ * - If the CPU has the ARM64_HARDEN_BRANCH_PREDICTOR cap, the
+ * hardening sequence is placed in one of the vector slots, which is
+ * executed before jumping to the real vectors.
+ *
+ * - If the CPU has both the ARM64_HARDEN_EL2_VECTORS cap and the
+ * ARM64_HARDEN_BRANCH_PREDICTOR cap, the slot containing the
+ * hardening sequence is mapped next to the idmap page, and executed
+ * before jumping to the real vectors.
+ *
+ * - If the CPU only has the ARM64_HARDEN_EL2_VECTORS cap, then an
+ * empty slot is selected, mapped next to the idmap page, and
+ * executed before jumping to the real vectors.
+ *
+ * Note that ARM64_HARDEN_EL2_VECTORS is somewhat incompatible with
+ * VHE, as we don't have hypervisor-specific mappings. If the system
+ * is VHE and yet selects this capability, it will be ignored.
+ */
#include <asm/mmu.h>
+extern void *__kvm_bp_vect_base;
+extern int __kvm_harden_el2_vector_slot;
+
static inline void *kvm_get_hyp_vector(void)
{
struct bp_hardening_data *data = arm64_get_bp_hardening_data();
- void *vect = kvm_ksym_ref(__kvm_hyp_vector);
+ void *vect = kern_hyp_va(kvm_ksym_ref(__kvm_hyp_vector));
+ int slot = -1;
- if (data->fn) {
- vect = __bp_harden_hyp_vecs_start +
- data->hyp_vectors_slot * SZ_2K;
+ if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR) && data->fn) {
+ vect = kern_hyp_va(kvm_ksym_ref(__bp_harden_hyp_vecs_start));
+ slot = data->hyp_vectors_slot;
+ }
- if (!has_vhe())
- vect = lm_alias(vect);
+ if (this_cpu_has_cap(ARM64_HARDEN_EL2_VECTORS) && !has_vhe()) {
+ vect = __kvm_bp_vect_base;
+ if (slot == -1)
+ slot = __kvm_harden_el2_vector_slot;
}
- vect = kern_hyp_va(vect);
+ if (slot != -1)
+ vect += slot * SZ_2K;
+
return vect;
}
+/* This is only called on a !VHE system */
static inline int kvm_map_vectors(void)
{
+ /*
+ * HBP = ARM64_HARDEN_BRANCH_PREDICTOR
+ * HEL2 = ARM64_HARDEN_EL2_VECTORS
+ *
+ * !HBP + !HEL2 -> use direct vectors
+ * HBP + !HEL2 -> use hardened vectors in place
+ * !HBP + HEL2 -> allocate one vector slot and use exec mapping
+ * HBP + HEL2 -> use hardened vertors and use exec mapping
+ */
+ if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR)) {
+ __kvm_bp_vect_base = kvm_ksym_ref(__bp_harden_hyp_vecs_start);
+ __kvm_bp_vect_base = kern_hyp_va(__kvm_bp_vect_base);
+ }
+
+ if (cpus_have_const_cap(ARM64_HARDEN_EL2_VECTORS)) {
+ phys_addr_t vect_pa = __pa_symbol(__bp_harden_hyp_vecs_start);
+ unsigned long size = (__bp_harden_hyp_vecs_end -
+ __bp_harden_hyp_vecs_start);
+
+ /*
+ * Always allocate a spare vector slot, as we don't
+ * know yet which CPUs have a BP hardening slot that
+ * we can reuse.
+ */
+ __kvm_harden_el2_vector_slot = atomic_inc_return(&arm64_el2_vector_last_slot);
+ BUG_ON(__kvm_harden_el2_vector_slot >= BP_HARDEN_EL2_SLOTS);
+ return create_hyp_exec_mappings(vect_pa, size,
+ &__kvm_bp_vect_base);
+ }
+
return 0;
}
-
#else
static inline void *kvm_get_hyp_vector(void)
{
diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 3baf010fe883..dd320df0d026 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -51,10 +51,13 @@ struct bp_hardening_data {
bp_hardening_cb_t fn;
};
-#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
+#if (defined(CONFIG_HARDEN_BRANCH_PREDICTOR) || \
+ defined(CONFIG_HARDEN_EL2_VECTORS))
extern char __bp_harden_hyp_vecs_start[], __bp_harden_hyp_vecs_end[];
extern atomic_t arm64_el2_vector_last_slot;
+#endif /* CONFIG_HARDEN_BRANCH_PREDICTOR || CONFIG_HARDEN_EL2_VECTORS */
+#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index bd8cc03d7522..a2e3a5af1113 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -58,7 +58,7 @@ config KVM_ARM_PMU
virtual machines.
config KVM_INDIRECT_VECTORS
- def_bool KVM && HARDEN_BRANCH_PREDICTOR
+ def_bool KVM && (HARDEN_BRANCH_PREDICTOR || HARDEN_EL2_VECTORS)
source drivers/vhost/Kconfig
diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 2deb6e9874c9..c712a7376bc1 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -151,6 +151,9 @@ void __init kvm_update_va_mask(struct alt_instr *alt,
}
}
+void *__kvm_bp_vect_base;
+int __kvm_harden_el2_vector_slot;
+
void kvm_patch_vector_branch(struct alt_instr *alt,
__le32 *origptr, __le32 *updptr, int nr_inst)
{
--
2.14.2
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